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    SubjectRe: Linux 2.6.29
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    On Friday 27 March 2009, Theodore Tso wrote:
    >On Fri, Mar 27, 2009 at 03:19:10PM -0400, Gene Heskett wrote:
    >> >You've said for a long that that ext3 is really bad in that it
    >> >inflicts this --- I agree with you. People should use other
    >> >filesystems which are better. This includes ext4, which is completely
    >> >format compatible with ext3. They don't even have to switch on
    >> >extents support to get better behaviour. Just mounting an ext3
    >> >filesystem with ext4 will result in better behaviour.
    >>
    >> Ohkay. But in a 'make xconfig' of 2.6.28.9, how much of ext4 can be
    >> turned on without rendering the old ext3 fstab defaults incompatible
    >> should I be forced to boot a kernel with no ext4 support?
    >
    >Ext4 doesn't make any non-backwards compatible changes to the
    >filesystem. So if you just take an ext3 filesystem, and mount it as
    >ext4, it will work just fine; you will get delayed allocation, you
    >will get a slightly boosted write priority for kjournald, and then
    >when you unmount it, that filesystem will work *just* *fine* on a
    >kernel with no ext4 support. You can mount it as an ext3 filesystem.
    >
    >If you use tune2fs to enable various ext4 features, such as extents,
    >etc., then when you mount the filesystem as ext4, you will get the
    >benefit of extents for any new files which are created, and once you
    >do that, the filesystem can't be mounted on an ext3-only system, since
    >ext3 doesn't know how to deal with extents.
    >
    >And of course, if you want *all* of ext4's benefits, including the
    >full factor of 6-8 improvement in fsck times, then you will be best
    >served by creating a new ext4 filesystem from scratch and doing a
    >backup/reformat/restore pass.
    >
    >But if you're just annoyed by the large latencies in Ingo's "make
    >-j32" example, simply taking the ext3 filesystem and mounting it as
    >ext4 should make those problems go away. And it won't make any
    >incompatible changes to the filesystem. (This didn't use to be true
    >in the pre-2.6.26 days, but I insisted on getting this fixed so people
    >could always mount an ext2 or ext3 filesystems using ext4 without the
    >kernel making any irreversible filesystem format changes behind the
    >user's back.)
    >
    > - Ted

    Thanks Ted, I will build 2.6.28.9 with this:
    [root@coyote linux-2.6.28.9]# grep EXT .config
    [...]
    CONFIG_PAGEFLAGS_EXTENDED=y
    CONFIG_EXT2_FS=m
    CONFIG_EXT2_FS_XATTR=y
    CONFIG_EXT2_FS_POSIX_ACL=y
    # CONFIG_EXT2_FS_SECURITY is not set
    CONFIG_EXT2_FS_XIP=y
    CONFIG_EXT3_FS=m
    CONFIG_EXT3_FS_XATTR=y
    CONFIG_EXT3_FS_POSIX_ACL=y
    CONFIG_EXT3_FS_SECURITY=y
    CONFIG_EXT4_FS=y
    # CONFIG_EXT4DEV_COMPAT is not set
    # CONFIG_EXT4_FS_XATTR is not set
    CONFIG_GENERIC_FIND_NEXT_BIT=y

    Anything there that isn't compatible?

    I'll build that, but only switch the /amandatapes mount in fstab for testing
    tonight unless you spot something above.

    Thanks.
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    --
    Cheers, Gene
    "There are four boxes to be used in defense of liberty:
    soap, ballot, jury, and ammo. Please use in that order."
    -Ed Howdershelt (Author)
    Losing your drivers' license is just God's way of saying "BOOGA, BOOGA!"



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